1. Field of the Invention
The present invention relates to a projection type image display device such as a liquid crystal projector adapted to guide light from a light source to an optical system to generate image light for magnification projection on a forward screen.
2. Description of Related Art
A conventional liquid crystal projector device includes a casing having disposed therein a light source and an optical system including a polarization beam splitter, a polarizing plate, liquid crystal panels, a projection lens, etc. A discharge emission lamp unit such as a metal halide lamp and an extra high pressure mercury lamp is used as the light source. As shown in FIG. 9, a conventional lamp unit 9 includes a light emitting tube 91 and a reflector 94 for reflecting light emitted from the light emitting tube 91 toward the optical system. The light emitting tube 91 has a spherical portion 93 providing a light emitting portion.
The light emitting tube 91 of the lamp unit 9 shown in FIG. 9 is cooled by a cooling fan because the temperature of the light emitting tube 91 exceeding a limit temperature would shorten the life of the light emitting tube 91. It is known that in light emission of the light emitting tube 91, the temperature at the vertically upper side of the light emitting tube 91 is higher than the temperature at the lower side thereof, which results in the temperature difference between above and below the light emitting tube 91. This temperature difference between above and below is the greatest at the spherical portion 93 of the light emitting tube 91. In order to fully bring out the performance of the light emitting tube 91, it is necessary to maintain the temperature of the light emitting tube 91 below the limit temperature, as well as to cool the light emitting tube 91 such that the temperature difference between above and below is held within a certain range.
Accordingly, the reflector 94 has an air introduction hole 95 for introducing air discharged from the cooling fan into the reflector 94, which is provided forward of a top end 92 of the light emitting tube 91 in an emission direction of light emitted from the lamp unit 9, and faces to the top end 92 of the light emitting tube 91, and also has an air discharge hole 96 for discharging the air introduced from the air introduction hole 95 outside the lamp unit 9, which is provided near a base end of the light emitting tube 91. A tongue 92a projects vertically downward from the top end 92 of the light emitting tube 91.
The tongue 92a blocks air to flow vertically downward of the light emitting tube 91 of the air introduced from the air introduction hole 95. Therefore, the air introduced from the air introduction hole 95 will mostly flow over the vertically upper side of the light emitting tube 91. This prevents the vertically lower side of the light emitting tube 91 from being excessively cooled, while allowing the high-temperature vertically upper side of the light emitting tube 91 to be sufficiently cooled (see JP 2003-123529, A).
In recent years, liquid crystal projector devices have been equipped with a higher-intensity lamp unit in order to satisfy a demand for higher intensity. This has been increasing a heat amount of the light emitting tube. However, the conventional lamp unit 9 shown in FIG. 9 has been suffering from a problem of difficulty in adjusting the air volume and air direction to provide a sufficient cooling effect for the highest-temperature spherical portion 93 of the light emitting tube 91 because the air introduction hole 95 is provided apart from the spherical portion 93 of the light emitting tube 91 to give a complicated airflow from the air introduction hole 95 to the spherical portion 93.
The air introduced from the air introduction hole 95 flows, as indicated by arrows in FIG. 9, through near the top end 92 of the light emitting tube 91 along the vertically upper side of the light emitting tube 91 to the spherical portion 93. Therefore, the air introduced from the air introduction hole 95 will take heat away from the light emitting tube 91 to have a high temperature, so that the high-temperature air will flow around the spherical portion 93 of the light emitting tube 91. This has prevented a sufficient cooling effect for the spherical portion 93, resulting in a problem of difficulty in maintaining the temperature of the spherical portion 93 of the light emitting tube 91 within the limit temperature.